The shrinking chess king demonstrated in the Rutgers study is made from a hydrogel. Though 73% water, the material retains a solid shape.

Transformation of the gel occurs in a bath of water. By gradually increasing the temperature up to 50°C, the king becomes dehydrated and shrinks. Likewise, as the temperature is decreased to around 11°C, the king swells back to its natural size.

The team also demonstrated how to add this shrinking/growing principle to specific parts of an object, rather than the whole thing. For example, the prongs of the claw can shrink and grow to close, but the body holding them together stays the same.

Parts of the 4D printed models can tuned to transform rather than the whole object. Image via Scientific Reports

3D microprinting process specifics

The 3D microprinter (termed the PμSL system) used in this study was custom-made by the Rutgers team. It consists of Liquid crystal on Silicone (LCoS) digital mask that exposes each layer to a different UV light outline; a projection lens; a UV LED; a linear stage; and a collimation device to control the UV beam width.

In the first step of printing, a digital 3D model was generated on CAD software and sliced into bitmap images. Each digital image was transferred to a digital mask to optically pattern ultra-violet (UV) light, which was projected on to prepared photo-curable PNIPAAm resin.

Through photo-polymerization, the patterned UV light converted the liquid resin into a solid layer. Once a layer was formed on the linear stage, it then dropped to expose the next layer.The process continued until the entire object was manufactured.

Diagram showing the preparation, PμSL, curing and shrinkage of the 3D printed hydrogel.

A medical shapeshifter and potential game-changer

“The full potential of this smart hydrogel has not been unleashed until now,” explains Lee, from the Rutgers School of Engineering. “We added another dimension to it, and this is the first time anybody has done it on this scale.”

The team is working on the micro-scale with this hydrogel, making objects with features ranging between 50 μm and 7 mm. The hope is that it can be used to develop new biomedical devices, like cell scaffolds, that help promote tissue growth, or even drugs with a precisely controlled released period, potentially giving patients more than one dose over time.

“If you have full control of the shape, then you can program its function,” Lee adds, “I think that’s the power of 3D printing of shape-shifting material,”

Beau Jackson is Senior Journalist at 3D Printing Industry. With a longstanding commitment to the site's content, she is credited with producing more articles than any other author in its history. Well-versed in the latest 3D printing research and legal/regulatory challenges, her repertoire spans aerospace, automotive, maritime, medical and creative industries. She is a keen speaker and active representative of the company at key additive manufacturing events.